This invention relates to a method for making brake drums and an apparatus therefor.
Brake drums for vehicular braking systems have machined cylindrical inner surfaces that form the engaging surfaces for the brake shoes. The axis of rotation of the drum is determined by one or more locating holes formed in the drum center. It is important that the machined cylindrical surface be truly concentric with the locating hole or holes. Conventionally it has been the practice to machine the cylindrical inner surface first and then form the locating holes subsequently. Since the loading of the tool on the part during te machining operation is quite heavy, large clamping forces must be employed to hold the drum during its machining operation. This results in frequent damage to the clamping tools and/or distortion of the drum during machining. Either of these factors results in the cylindrical surface being formed eccentrically and imbalance conditions result. Quite frequently the degree of imbalance is so great that it is impossible to balance the drum and it must be scrapped.
It is, therefore, a principle object of the invention to provide an improved method for making brake drums or the like.
It is another object of the invention to provide an improved apparatus for manufacturing brake drums.
It is a still further object of the invention to provide an improved method and apparatus for manufacturing brake drums with a high degree of accuracy.